1. Field of the Invention
The invention concerns an information carrier, in which information is contained in the form of a hologram.
2. Discussion of the Background Art
Such information carriers frequently serve as security seals, for example, for characterizing trademark products (electronic components, computer components, pharmaceutical products, image, audio and data media, clothing articles, etc.). There is also a requirement for security against counterfeiting in the case of bank notes. For this purpose, information is introduced onto an information carrier in the form of a hologram by means of appropriate and expensive methods. This information then cannot simply be copied by means of a conventional copying machine (e.g., for copying printed paper) onto another information carrier.
Frequently, information is stored either in the form of a transmission hologram or in the form of a reflection hologram, on pieces of foil that are in turn glued onto products for purposes of protection against copying. These so-called security seals serve for authenticating the marketed product. Depending on the angle of lighting and the viewing angle each time, the observer perceives different colors, patterns and motifs. The construction of these foil layers and the technical expenditure in their production offer a meaningful protection against simple copying and thus marketing of counterfeit products with the copied security seal. A copying of film holograms or volume holograms, which have stored the information in a high-resolution photo layer, can basically be accomplished only with expensive laser equipment, which can supply the coherent light that is necessary and sufficient for copying.
In the case of the known information carriers with holograms, despite the measures taken, there is always a need to further increase the protection against copying.
The object of the invention is to create an information carrier of the type named initially with increased copy protection and/or an additional easily recognizable security feature.
The invention solves this object with the subject of claim 1.
Preferred examples of embodiment of the invention are described in the dependent claims 2 to 9. In addition, preferred methods for the production of such information carriers according to the invention are described in claims 10 to 14.
According to claim 1, the hologram in an information carrier of the type named initially is the combination of a transmission hologram and a reflection hologram.
The information carrier may be comprised, among other things, of any of the initially named materials, for example, a foil (e.g., in the form of a security seal) or a more solid-type material, which is partially transparent upon examination, or contains the combination of a transmission hologram and a reflection hologram in at least one intermediate layer lying inside the material. The information carrier may also be part of a larger design of information carriers, which comprise, for example, collateral sheets, bank notes, credit cards, packagings, labels, images, etc., with additional printing. Additional information, which is for the most part visible (i.e. can be read or presented with light in the optically visible region) can also be printed or otherwise introduced onto these materials. However, information in the optically invisible range can also be contained therein (e.g., information that can be read with UV or IR light).
In addition, the information contained in the respective type of hologram (transmission or reflection hologram) can be stored in an optically visible manner (i.e. recognizable upon irradiation with visible light) or in an invisible manner (e.g., recognizable only upon irradiation with UV light or IR light). The information itself may be contained as a three-dimensional hologram (volumetric reproduction of an object in a complete three-dimensional reproduction), a two-dimensional/three-dimensional hologram (flat motif with a three-dimensional background), two-dimensional hologram (flat graphic), etc.
The information may also comprise purely geometric or irregular, (apparently) random patterns. For example, the transmission hologram may contain information in the form of one or more uniform surfaces, which iridesce, for example, only in rainbow colors upon irradiation with white light. This xe2x80x9cplay on colorsxe2x80x9d represents information in the sense of the invention.
Basically, holographically stored information of film or volume holograms is meaningfully protected from copying, since coherent light sources must be used for such copying. In addition, the combination of the two hologram types into one hologram according to the invention offers the following additional advantages: either one or the other or both holograms appear each time depending on the lighting (from the front or from the back) with respect to the information carrier, or depending on the angle of lighting and the angle of viewing when a reflector-type transmission hologram or raised hologram is used in combination with the reflection hologram. The two types of holograms can be clearly differentiated from one another on the basis of their characteristic apparent images, so that, in principle, it is not possible to imitate the xe2x80x9cmotifxe2x80x9d of one type of hologram by an identical pattern in the form of the other type of hologram. One of the hologram types can thus serve as the xe2x80x9cwatermarkxe2x80x9d for the other type of hologram. Thus, e.g., with normal viewing, only one type of hologram may be visible, while the other appears only under specific conditions (depending on the light wavelength or the angle of incidence of the reconstruction light, etc.), which are known only to the initiated. Copying is made even more difficult, since the two types of holograms must be copied in different ways each time. Thus, for example, the xe2x80x9cconcealedxe2x80x9d type of hologram is not automatically copied when the visible type of hologram is copied, so that the copy no longer contains the xe2x80x9cconcealedxe2x80x9d hologram type.
According to a first example of embodiment, the combination of the two types of holograms preferably consists of the fact that the transmission hologram and the reflection hologram are contained in two separate hologram layers, wherein the two hologram layers are arranged one on top of the other, and at least one hologram layer is transparent. Also, with this layering of two hologram layers, both types of hologram appear simultaneously, as long as the upper layer of the hologram lying closer to the readout side of the information carrier is transparent.
According to a second example of embodiment, the combination consists of the fact that the transmission hologram and the reflection hologram are contained together in a single hologram layer. For the production of such an information carrier, preferably both types of holograms are recorded simultaneously or the transmission hologram is recorded first and then the reflection hologram, or vice versa. Alternatively, in the production of the information carrier according to the second example of embodiment, the transmission hologram and the reflection hologram can be recorded by alternating pixels or alternating lines. This pixel-type or line-type recording can be produced preferably either by means of an appropriate mask, wherein the transmission hologram and the reflection hologram are then recorded sequentially in time, or by means of a controlled light beam.
The reflection hologram is preferably designed in such a way that it serves for a one-color, multi-color or true-color illumination of the transmission hologram. Advantageously, nearly any type of transmission hologram (not only in the form of rainbow holograms, among other types) can be rendered in a true-color manner also with sufficiently sharp contrast.
If the carrier material of the information carrier is not light-transparent, a layer is provided that back-reflects light into the hologram layer or layers on one side of the two hologram layers or the single hologram layer. The light striking the information carrier over the considered surface passes through the hologram layer(s) containing the combination of the two hologram types and is reflected back into the hologram layer(s) by the reflecting layer. The reconstruction light beam thus arrives, so to speak, also from behind into the hologram layer(s). Advantageously, the usual transmission hologram (which normally requires reconstruction light striking from behind) can be viewed with reconstruction light striking from in front by means of this measure.
Advantageously, the transmission hologram and/or the reflection hologram is contained in such a way that it is visible only under one or more specific viewing angles. Advantageously, one of the hologram types, as a simple recognizable optical security seal, like a watermark in a banknote, can increase the clear and reliable recognizability of the original product provided thereby. In addition, different motifs or pieces of information can be visible each time in the transmission hologram and/or the reflection hologram, depending on the viewing angle (sequence of motion when the information carrier is inclined relative to the lighting source).
Preferably, the information of the transmission hologram and/or the reflection hologram at least partially comprises coded information. In addition to the directly recognizable information, further information may be contained, which can be recognized only with a specific decoding key, which is contained, for example, on another information carrier as a master key, or is visible only with the use of several reconstruction beams in a specific angular arrangement.
Preferably, the coded information of the transmission hologram is the decoding key for the coded information of the reflection hologram, or vice versa. In this way, the coded information is only decoded and thus visible if the other type of hologram is also still completely present. A decoding key, which lies above the motif only as a uniform xe2x80x9cgray smearxe2x80x9d or the like and is thus not recognizable as a key, can be contained in one of the hologram types, for example, in addition to its own recognizable motif. The decoding key appears and decodes the coded information of the other type of hologram only upon irradiation of the information carrier with a specific wavelength (e.g., in the optically invisible region) or at one or more specific angles. In addition, the latter type of hologram may contain still additional uncoded information, which is optically visible, in addition to the coded information. Thus, in the case of an impermissible copying of the information carrier, the decoding key is not copied (since, for example, the wavelength range or the one or more reconstruction angles are not known, with which the decoding key and/or the coded information are redorded), and the coded information of the unauthorized copy is no longer decoded upon irradiation with the specific wavelength.
Preferably, a transparent copy-protection layer with a property that rotates the polarization of the readout light and/or a filtering property is introduced onto the viewing surface. The advantage of this copy-protection layer lies in the fact that it cannot be recognized, for example, with the naked eye. If the information carrier is now photographically or holographically copied, then the copy no longer contains this copy-protection layer. A polarization foil (or a corresponding polarizer) placed over the copy and the original can differentiate between the two of them with appropriate alignment, since the original darkens at a specific alignment of the polarization foil. If copied with polarized light, with specific alignment, the information of the original, for example, generally cannot be read out. For other embodiments of the copy-protection layer, reference is made to the German Patent Application 199 04 282.9, the disclosure content of which is fully incorporated herewith in the present application. The advantageous examples of embodiment described therein of the copy-protection layer with the information carrier having a hologram may be used alternatively or together with the two types of holograms. Thus, for example, the coded information of the reflection hologram, either alone or in combination with the coded information of the transmission hologram, can be a decoding key for the coded information of the copy-protection layer, or vice versa. To the person with average skill in the art, it is self-evident with a combination of three possibilities (copy-protection layer plus two types of holograms), each of which may contain coded information for a decoding key, to combine two of these randomly, so that the combination of the two together comprises the coded information or the decoding key. Alternatively, one type of hologram does not participate in the coding or decoding.
Particularly preferred: when the information carrier is used as a security seal, the (coded) information of the transmission hologram and/or the reflection hologram contains at least partially individualized information. Thus, when producing security seals, it may be of advantage to introduce, for example, continuous serial numbers in the security seal.